Water quality, diatom species composition and biomass estimates were performed in the Gharasou River in western Iran. Five sites along the River Gharasou were sampled every month from April to September 2005. Physical and chemical factors (pH, NO 3 -N, PO 4 -P, dissolved oxygen, total suspend solids, total dissolved solids, conductivity, turbidity, chemical oxygen demand and biological oxygen demand) were measured along with biological properties of the periphyton including biomass, ash-free dry mass, chlorophyll-a concentration and the taxonomic composition diatom assemblages. Information from the diatom assemblage was used to calculate the Trophic Diatom Index and biovolume. The TDI was significantly correlated with measures of human disturbance at the sites (e.g. PO 4 -P, NO 3 -N and dissolved oxygen) as well as to biomass measures (chlorophyll a, ash-free dry mass and biovolume). The sensitivity of the TDI and its component metrics to environmental stressors supports the use of this index for monitoring ecological conditions in streams in Iran and to aid diagnosis of the cause of their impairment.

No abstract

Indoor artificial streams were used to evaluate the short-term (24 day) influence of copper and zinc, individually and in combination, on the biomass and taxonomic composition of algal periphyton communities. The effects of Cu (50 µg l -1 ) and Zn (1 mg l -1 ) were assessed using measurements of biomass, ash-free dry mass (AFDM), chlorophyll-a concentration, taxonomic composition and biovolume. In artificial streams with Cu, Zn and Cu+Zn, there were significant (p < 0.05) reductions of chlorophyll-a concentrations, dry mass and AFDM, and also changes in * Corresponding author: islam.atazadeh@gmail.com the species diversity and relative abundances of periphyton species. In artificial streams containing both Cu and Zn the taxonomic composition shifted from a Cyanophyceaen dominated community to one consisting mainly of Chlorophyceae, whilst the relative contribution of Bacillariophyceae was not significantly altered.

Stauroneis pachycephala was described in 1881 from the Baakens River, Port Elizabeth, South Africa. Recently, it was found during surveys of the MacKenzie River (Victoria, Australia), the Florida Everglades (USA), and coastal marshes of Louisiana (USA). The morphology, ecology and geographic distribution of this species are examined in the present paper. This naviculoid species is characterised by lanceolate valves with a gibbous centre, a sigmoid raphe, an axial area narrowing toward the valve ends, and capitate valve apices. The central area is a distinct stauros that is slightly widened near the valve margin. The raphe is straight and filiform, and the terminal raphe fissures are strongly deflected in opposite directions. Striae are fine and radiate in the middle of the valve, becoming parallel and eventually convergent toward the valve ends. The external surface of the frustule and copulae is smooth and lacks ornamentation. We also examined the type material of Stauroneis pachycephala. Our observations show this species has morphological characteristics that fit within the genus Envekadea. Therefore, the transfer of Stauroneis pachycephala to the genus Envekadea is proposed and a lectotype is designated.

No abstract